1. Field of the Invention:
This invention relates to light measuring devices for cameras with means making it possible to change over the light measuring area as the reflected light from the film surface or the shutter surface is sensed.
2. Description of the Prior Art:
It is known in the art to provide for the type of light measuring device using the reflected light from the film surface or the shutter surface with means making it possible to change over the light measuring area as disclosed in U.S. Pat. No. 4,180,312.
Such a conventional light measuring area changeover means is constructed in the form of two optical systems arranged ahead of the photosensitive element which systems are selectively inserted into the light measuring optical path thereby changing the light measuring area.
The aforesaid conventional means operates an optical system comprised of lenses placed in front of the photosensitive element, therefore, the provision of three or more interchangeable light measuring areas cannot be made without involving an increase in the complexity of structure.
The aforesaid patent also discloses a technique of preventing the illumination impinging on the photosensitive element from changing as the light measuring area changes by using a gray flat plate or a gray wedge for one of the optical systems. However, when applied to the device having many interchangeable light measuring areas, this technique also creates a large problem, namely controlling the densities of the correspondingly increased number of gray flat plates or wedges.